Process for precipitation of uranium from solution



Sept. 24, 1963 J. L. HART ETAL 7 3,104,941

PROCESS FOR PRECIPITATION OF URANIUM FROM SOLUTION Filed Oct. 26, 1959 2Sheets-Sheet 1 FROM CLARIFIER BAslc 7- H PRECIPITANT PREGNANT l uo 2l-SET POINT I6 43 |2I-- [i F 2.

l9 K i as as v .21. I4 24 44 -'--EE\ 5 :F/N ANK T'TRA T T0 FILTERSPRECIPITATION & RECOVERY TANK 36 5 l6 SETPOINT 3| as L..

IQN II F WV 30 441 47 INVENTORS J.L.HART 49 P R.A.KOBLE FIG. 2 M

ATTORNEYS Sept. 24, 1963 J. L. HART ETAL Filed Oct. 26, 1959 2Sheets-Sheet 2 g/L NaOH TOTAL SODHJMION PRESENT AS CARBONATE ANDBICARBONATE 47.5 /1.

FIG. 3

TITRE 9 6 g/L NclHC03 INVENTORS J. L. HART R. A. KOBLE A T TORNEKSUnited States Patent M 3,1945% PROQESS FOR PRECEPITATHON 0F URANiUli iFROM SOLUTEON James L. Hart and Robert A. Koble, Bartiesville, Okla,

assignors to Phillips Petroieum Company, a corporatron of Delaware FiiedOct. 26, M59, Ser. No. 848,782 18 Claims. (Q1. 23-145) This inventionrelates to improvements in processes for uranium recovery byprecipitation of the uranium values from a solution in which they havebeen dissolved.

One method of recovering uranium values from the ores in which theyappear involves leaching the ore and subsequently recovering the uraniumvalues from the liquor formed in leaching. When the ore has a highlimestone content, the leaching is accomplished by contacting the orewith a carbonate leach solution in order to leach out the uraniumvalues. Ores treated in this manner include but are not limitedtocarnotite, coffinite, uraninite and the like. This process ishereinafter termed the carbonate leach process.

The carbonate leach process for extracting uranium values from orebriefly comprises Wet grinding the crushed ore in the presence of sodiumcarbonate and sodium bicarbonate, oxidizing and leaching a resulting oreslurry containing about 50 percent solids to dissolve uranium values asthe sodium uranyl tricarbonate complex to form a pregnant liquor thatcontains the uranium values, filtering the pregnant liquor to remove thetailings therefrom, clarifying the pregnant liquor after filtering, andthereafter precipitating the uranium from the pregnant liquor andrecovering the uranium in the form of U 0 from the precipitate. One ofthe methods for eifecting the precipitation is to increase the pH untilthe uranium precipitates as sodium diuranate (N'clzUzOq). Ordinarily,filtering is employed to separate the precipitate from the liquid inwhich it appears. The filtrate recovered by this last step of filteringis called the barren liquor and contains some very small quantity ofuranium values as well as other chemical values and is recycled for usein the process. Preferably, the barren liquor is recarbonated usingcarbon dioxide to regenerate the carbonate and bicarbonate values insolution.

carried out by adding a suitable material, such as sodium hydroxide, inone single step to the pregnant liquor. The

amount added is sufiicient to neutralize the bicarbonate solution and toprecipitate the uranium values. However, the amounts of bicarbonate anduranium present in the pregnant liquor vary somewhat from time to timeand therefore the prior art method sometimes'results in incompleteprecipitation and recovery of uranium, and at other times results in theuse of too much hydroxide.

Accordingly, it is an object of our invention to provide an improvedmethod of adding the precipitating agent to a solution having uraniumvalues therein. More particularly, it is an object of'our invention toprovide an improved method in the carbonate leach process for adding theprecipitating agent to a clarified pregnant liquor. Another object ofour invention is to provide a method of automatically controlling theaddition of a precipitating agent to solutions having uranium valuestherein, and in particular to automatically control such addition in thetreatment of clarified pregnant liquors produced in the course of thecarbonate leach process. Another object of our invention is toaccomplish the foregoing objects to secure either or both of theadvantages of reduced re- 1 quireme nts for precipitating agents andincreased recovery of uranium from the solution so treated.

In connection with accomplishing these objects it is a 3, i hifi i-iPatented Sept. 24, 1963 principal feature of our invention that theprecipitating agent is added in two stages, with sufiicient quantitybeing added in the first stage to substantially neutralize thebicarbonate ions in the pregnant liquor. At or near this point in thefirst stage (zero bicarbonate point), a small change in the amount ofprecipitating agent produces a ver large change in the pH. In the secondstage is added a sufficient quantity of precipitating agent toprecipitate the uranium values from the solution.

Other objects, advantages and features of our invention will becomeapparent from the following description and the drawings appendedthereto.

In the drawings:

FIGURE 1 is a schematic flow diagram of a preferred embodiment for thepractice ofour invention;

FIGURE 2 is a schematic diagram of another embodiment for the practiceof our invention;

FIGURE 3 represents typical curves of the titre (abscissa) plottedagainst the pH (ordinate).

As previously mentioned, the principal feature of the invention involvesthe process of adding the precipitating agent in two stage The additionto the first stage increases the pH of the solution treated up to apredetermined point. No precipitation takes place in the first stage. inthe second stage there is added sufiicient additional agent to causeprecipitation. In both stages of adding the agent, thorough mixing andagitation of the mixture is carried out. Preferably, the invention isapplied to the treatment of pregnant liquor as produced in the carbonateleach process. However, our invention can also be applied to thetreatment of other liquid streams produced in the course of extractinguranium with the carbonate leach process.

The liquors are formed in the above-mentioned slurrying step by mixingan alkali metal carbonate with water and subsequently contactinguranium-containing ore therewith under oxidizing conditions. Normally,in leaching uranium values by the carbonate leach process, sodiumcarbonate and sodium bicarbonate are employed. However, while not aseconomical as the sodium compound, other alkali metal carbonates andbicarbonates (e.g. potassium, lithium, rubidium and cesium) can beemployed.

The pregnant carbonate leachliquors from which the uranium values areprecipitated by operating according to our invention will generallycontain from 0.5 to 15 grams per liter of U 0 usually from 2 to 3 gramsper liter on the same basis. The uranium in these carbonate leachliquors is present as Na UO (CO but is normally expressed in terms of U0 The pregnant carbonate leach liquors are mixed with the precipitatingagent at a temperature within the range extending tfirom 50 F. to 200preferably from F. to 176 F, and more preferably from F. to F.

Precipitation is brought about by introducing an alkali metal hydroxideinto the pregnant liquor. Although the alkali metal hydroxide may beadded in solid form, it is preferred to add it as an aqueous solution.While sodium hydroxide (NaOH) is to be preferred in making up theaqueous solution, the hydroxides of the other alkali metals (potassium,lithium, rubidium, and cesium) can be employed for this purpose. Theaqueous solution which is employed will normally contain from 10 to 75,preferably 20 to 60- percent by weight of alkali metal hydroxide andmore preferably from. 40 to 60 percent by weight. In the process of thisinvention, it is contemplated that the hydroxide of the same alkalimetal as used in the leach step is employed to bring about theprecipitation of uranium values from the leach liquors, i.e. sodium hydroxide is used to precipitate sodium carbonate leachv solutions,potassium hydroxide is used to precipitate potassium carbonate leachsolutions, and so forth.

In the leachin of uranium-containing ore by the carbonate leach process,the uranium content of the ore will vary, and wide variations in the oreto leach liquor ratio are possible. As a result, pregnant liquorscontaining from 0.5 to. grams per liter of U 0 are obtained. Toprecipitate these uranium values from solution, it is necessary toneutralize the bicarbonate present and to provide excess alkali metalhydroxide. In the present pnocess, depending upon the concentration ofdissolved sodium urainyl tricarbonate in the leach liquor, the amount ofsodium hydroxide, for example, required in excess of the zerobicarbonate point will be within the range between 2.0 and :grams perliter NaOH. The larger amounts of NaOH are required for more dilute U 0solutions and smaller amounts for the more concentrated solutions. Atypical pregnant leach liquor containing from 2.5 to 2.75 grams perliter U 0 requires an excess of 4.5 to 5.0 grams per liter NaOH inexcess of the Zero bicarbonate point [for precipitation.

After the precipitation is accomplished, the. liquorprecipitate mixtureis then filtered and the uranium values are recovered from the filtercake.

FIGURE 1 shows a preferred embodiment of the invention wherein clarifiedliquor is received from a conduit 1G and delivered into a tank ll fortemporary storage. Although not shown, this liquor is received from theelarifier which is located upstream of the apparatus illustrated in bothFIGURE 1 and FIGURE 2. The tank 11 is located physically above thesubsequent tanks and vessels into which the pregnant liquor is directedso that gravity flow can take place. The pregnant liquor flows out ofthe tank 11 through a conduit 12 and is delivered into a titration tank14. Flow measuring apparatus such as the orifice plate 15 and the flowrecorder 1d are connected in conduit 12. A normally open manually opeated valve 17 may also be disposed in this line, as an optional feature.

The titration tank 14 comprises the titration zone wherein the firstportion of precipitating agent is added. For ease of explanation, itwill be assumed that sodium hydroxide is employed as the precipitatingagent. The sodium hydroxide is introduced into the titration tank fromthe conduit 19 which connects to tank 2i) by means of the conduit 21.The tank is located physically above these vessels in the system Wheresodium hydroxide is added to the uranium containing liquor, in order toachieve a gravity flow into these other tanks. An agitating means, suchas impeller 22, driven by a motor 23, and supported by appropriate means.(not shown) is disposed in the titration tank 14. The titration tank isof a relatively small volume so that it can cooperate with the impellerin order to [facilitate a thorough mixing of the pregnant liquor withthe hydroxide. In the preferred embodiment, the conduit 19 dischargesthe hydroxide at a region Olf high turbulence within the tank, such asthe eye of the impeller 22.

While the above-mentioned alkali metal hydroxides are the preferredprecipitating agents, it is also Within the scope of this invention toemploy the oxides and hydroxides of calcium and magnesium in the first(titration) stage. The alkali metal hydroxides are absolutely necessaryin the final (precipitation) stage. If the oxides and hydroxides ofcalcium and magnesium are employed in the first stage, it is necmsary tofilter out undissolved and unreacted precipitating agents andprecipitated carbonates between the first and second stages.

- The admixture flows from titration tank 14 through a Weir chamber 24,thence into the precipitation tank 25 through the conduit 26. Tank 25may comprise one tank or a series of precipitation tanks, which ineither case is a precipitation zone and is equipped with agita ing meanssuch as the impeller 28 and motor 29. The precipitating agent isintroduced into 25 by means of conduits 21 and 30. It is preferred thatthe sodium hydroxide be introduced into region of high turbulence in theprecipitation tank tfor substantially the same reasons set forth abovewith respect to tank 14. Manual valves, e.g. 32, normally open, aredisposed where desired. Reaction products are Withdrawn from the tank 25by means of conduit 31 and circulated to filters (not shown) locateddownstream thereof. The uranium product is recovered from the filtercake in the subsequent processing.

An automatic control system is provided in order to perform the functionof automatically controlling the addition of the precipitating agent tothe pregnant liquor in the titration tank T4 and to the mixture in theprecipitation tank 25. This system includes two control loops. The firstcontrol loop comprises the means for controlling the addition of causticin the first stage by measuring the pH of the admixture withdrawntherefrom in order to produce the first control signal and thenadjusting the rate at which the sodium hydroxide is added in the firststage responsive to the control signal. The second loop comprises ameans for measuring the ratio of the rate at which pregnant liquor isintroduced into the system to the rate at which sodium hydroxide isintroduced into the precipitation tank in order to produce a controlsignal representative of the change requircd and then to adjust the rateat which the hydroxide is introduced into the second or precipitationstage responsive to this control signal. The first loop comprises a pairof electrodes 35, 3&5 disposed in the weir chamber 34- and connectedthrough a combination of a computer an amplifier to a pH recordercontroller 46. The computer-amplifier 38 is preferably an electronicdevice which responds to signals from the electrodes 35 and 36 byproducing the antilogarithm of the pH represented by such signals. Anelectronic system suitable for this purpose disclosed in Rev. Sci.Instr., 2l:l79l8 l (1950) and is referred to in Soroka Analog Methods inComputations and Simulation (McGraw-Hiil, New York, 1954), pages 66-67.The reason for providing this feature is so that the controller 48 canprovide a linear response that is appropriate to the pH that is detectedby the electrodes 35 and 36. The linearized pneumatic output signalproduced by the pH recorder controller 40 is then transmitted to a motorvalve 41 to adjust the amount of precipitating agent introduced in thefirst stage.

The second control loop includes the flow measuring apparatus measuringthe flow of the pregnant liquor, elements l5 and 16. A pneumatic outputsignal from 15 and 16 is provided to a how ratio recorder controller 43as one of the input signals thereto. A similar flow measuring devicecomprising the orifice plate 44- and the how recorder 45 determines theflow of precipitating agent into the second stage (precipitation tank25) and transmits a pneumatic output signal from 45 to the ratiocontroller 4-3 as a second input signal for the latter. A pneumaticcontrol signal is produced by 43 and is transmitted to motor valve d7 toadjust the flow of caustic into the second stage.

FIGURE 2 is generally similar to FIGURE 1 and similar apparatus isdenoted by like reference numerals. The main difference is that the flowof the titre liquor withdrawn from the titration tank 14 is measured bythe flow measuring apparatus 15' and T6 in order to provide one of theinput signals to the ratio controller 4-3. This flow measurement istaken instead of the flow out of the tank 11 as in FIGURE 1. Manualvalves, optional features, are not shown here. The other differenceshere are that the tanks 11 and 2d are not disposed for gravity how, andtherefore pumps 48 and 49, respectively, provide the means forwithdrawing the various liquids from the two tanks and delivering themto their respective destinations. Because of the modifications of theapparatus in this figure, primed numbers are used to denote thoseelements serving substantially the same function but which have beenaltered in the manner described in this paragraph.

. Constructions of suitable pH and flow measuring means,recorder-controllers, and the like are shown in Considine, ProcessInstruments and Control Handbook, McGraw- Hill (New York), 1957.

The phenomenon set forth in FIGURE 3 facilitates an understanding of thecooperation between the two control loops and of the reason for addingthe precipitating agent in two distinct stages. This figure shows thatfor a given solution an S-shaped curve is produced as it moves from theexcess bicarbonate state to the more basic state of excess caustic. Thiscurve is made by studies on carbonate leach process pregnant liquors. Itshows that at the zero bicarbonate point (denoted by the titre value ofthere is an inflection point disposed in the curve. It also shows in theregion of this inflection point, from pH values of 10.8 to 11.7, a verygreat change in pH is accomplished by a very small change in titre.Translated to the terms of our invention, this curve demonstrates that avery small addition of hydroxide will give a very great change in pH inthe neighborhood of the zero bicarbonate point. A pH controller can, bybeing limited to controlling in the inflection point region, operate atan optimum or maximum sensitivity. It is for this reason that the pH iscontrolled at this particular range of values in the titration zonerepresented by the tank 14. A very sensitive and accurate control isthus achieved in the first stage.

In FIGURE 3, a number of curves are plotted which contain diiferentamounts of sodium carbonate and sodium bicarbonate. That is, both thetotal of carbonate and bicarbonate vary, and the ratio of carbonate tobicarbonate varies. Since these curves converge at the zero bicarbonatepoint, it can be seen that by limiting the set point of the first loopto near the zero bicarbonate point, the control problems in determiningtotal sodium ion concentration and carbonate/bicarbonate ratio areeliminated, while gaining improved sensitivity to pH change.

Experience has shown precipitation does not occur until the pH reaches avalue of at least 11.8, and with the solutions of FIGURE 3, at a pH ofapproximately IZLZ. Higher values than 12.2 may be required in order toprecipitate a sufficient quantity of the uranium values. Since the pH isrelatively insensitive to changes in the alkali metal hydroxide contentin this region of preclpitation, the second control loop does not relyon measurement of the pH but instead relies on a controlled ratio ofHow. This ratio is that of tne flow of liquid through line 349' to theflow through either one of lines 12 or 26-, or vice versa. With thiscontrol arrangement, the maximum sensitivity is realized in controllingtne first stage and the optimum accuracy of control is realized in thesecond stage. To demonstrate the superiority of the present process inmore accurately controlling tne addition of excess NaGl-l over methodsemploying pH alone, it should be pointed out that the pH changes onlyfrom 12.2 to 12.23 in going from g./l. excess NaOH to 28.8 g./l. excessNaOH. It is to be understood that the curves in FIGURE 3 arerepresentative and that the positions of these curves can varyvertically and/ or laterally with the temperature at which the reactionis carried out, the concentration of the uranium values and/or theimpurities in the pregnant liquor, and the concentration of the sodium,ions in solution produced in the respective titration and precipitationzones. It is to be further understoed that such variation is notsubstantial and that in any event the zero bicarbonate point is locatedin the pH range from 10.8 to 11.7.

In stanting up the system appropriate set points are selected for therespective controllers 4b and 43. In one embodiment, the respectivecontrollers are adjusted for set point values representing a pH of 11.0and a ratio of 0.0 1 gallon of 50 weight percent aqueous NaOH per gallonof pregnant liquor. The latter ratio is 5 selected to produce a solutionhaving at least 4 grams per liter of excess sodium hydroxide.

Once the controllers are adjusted, the system is started up and operateduntil the solution in titration tank 14 is brought near or to itscontrol (set) point. The system is operated manually until this isaccomplished. Once this condition is reached, the system is thenswitched to automatic control. Then, the pH of the solution is measuredas it leaves the titration tank through the weir chamber 24-. Thequiescent conditions in the weir chamber promote accuracy of measurementby the pH electrodes and their associated apparatus. An electricalsignal representative of the pH is produced at the electrodes, islinearized in =38, then is fed into recorder controller 49 where it iscompared with a signal representing the set point, and from thecomparison a control signal is produced. This control signal, sometimestermed an error signal, normally represents the difference between themeasured, linearized pH and the set point. It is transmitted to themotor valve 41 and produces an adjustment in the flow of the causticinto the titration tank 14. This adjustment is commensurate with thedirection and magnitude of the difference between the set point and themeasured value of the pH.

In similar fashion, the second stage is manually brought to its controlpoint and the controller as is then put on stream. The flow controllerreceives flow measurements from the respective apparatuses 15 and 1.6(or 15' and 16) and 44, 45 and by determining the ratio between thesetwo rates of flow and then comparing it with the set point of the ratiocontroller, a ratio control signal is produced. This control signal isthen transmitted to the motor valve 47 which makes the requisiteadjustment in the amount of alkali metal hydroxide that flows into thetank 25 per uni-t time.

By way of further explanation, when the pH of the mixture in 24 is abovethe set point, the pH controller 40 operates to reduce the flow in line19 by means of valve 41; an opposite reaction is produced if the pH ofthis stream is below the set point. The ratio controller operates toincrease the flow in line 38' by means of motor valve 47 if the ratio ofthe pregnant liquor flow rate to the precipitating agent flow rate isabove the ratio set point.

- The following example will further illustrate the practice of myinvention:

Example In a commercial plant wherein uranium-containing ore is leachedwith carbonate-bicarbonate leach solution, the rate of flow of clarifiedpregnant leach liquor to the precipitation unit is 180 gallons perminute of solution containing 2.76 grams/liter (0.00 161 pound/gallon)of U 0 The pH of this solution is 9.6, and the solution contains 15grams per liter NaHCO and 40 grams per liter Na CO This temperature ofthe solution is F. This solution is then admixed with 50% by weightaqueous sodium hydroxide which is admitted through a line in which ismounted a diaphragm motor valve. This valve is controlled by a pH recor-e-r controller measuring the pH of the solution after sodium hydroxideaddition. The set point of the pH controller is 11.6. The rateof sodiumhydroxide addition to achieve this pH is approximately 1.70 gallons of50% by weight aqueous NaO-l-I per minute.

The solution of 11.6 pH is then admixed with additional 50% by weightaqueous NaOl-l as controlled by a ratio flow controller receivingresponses from orifices mounted in both the 11.6 pH solution line andthe caustic line (=e.g., FIGURE 2). Based on the flow rate of 181.7gallons per minute of the mixture, the ratio flow controller adjusts theaddition of NaOH to approximately 1.20 gallons per minute of 50% byweight aqueous sodium hydroxide. This provides a five gram per literexcess of sodium hydroxide and causes the precipitation of sodiumdiuranate in an easily fiherable form.

In a plant where the throughput is 2000 tons per day of ore that istreated by the carbonate leach process, a reduction in sodium hydroxiderequirements of at least 3 tons per day is achieved by our inventionwhen com pared with one prior art control system. This particular priorart control system employed identical solutions, the hydroxide was addedin a single stage, and the liquid streams Were controlled by flow ratecontrollers.

From the foregoing description and appended drawings it should beapparent that we have provided a novel and useful invention for thecarbonate leach process that comprises adding the precipitation agent intwo steps. Other features of this invention comprises automaticallycontrolling the amount of sodium hydroxide added to the pregnant liquorin the first stage to increase the pH to a value in the general vicinityof the zero carbonate point, e.g. 10.8 to 11.7. Another feature isautomatically controlling the rate at which caustic is added in thesecond stage by the employment of a ratio flow controller which operatesin response to the ratio of either the rate at which pregnant liquor issupplied to the first stage or to the rate of flow of solution into thesecond stage, to the rate of flow of the caustic into the second stageof addition.

While we have described our invention with respect to certain specificembodiments, reagents and the like, it is not our intention to belimited to those specific mean which have been described. It is ourintention to include as our invention all the subject matter asdisclosed herein and also to include as our invention thosemodifications thereof which will be obvious to one skilled in the art.One example of these modifications would be to employ a completelyelectric control system, using electric recorders and electric recordercontrollers.

We claim as our invention:

1. An improved process for precipitating uranium values from a clarifiedpregnant liquor formed by leaching an ore with a carbonate leachsolution, said process comprising feeding a stream of clarified pregnantliquor at a first rate of flow to a titration zone; feeding a stream ofaqueous sodium hydroxide at a second rate of flow to said titrationzone; mixing said hydroxide with said liquor in said zone to form amixture having a pH in the range from 10.8 to 11.7; measuring the pH ofsaid mixture and comparing it with a preselected pH in said range toproduce a control signal representative of the change in the rate ofsaid feeding of hydroxide to produce a mixture of said preselected pH;changing said second rate of flow in response to said control signal; ata third rate of flow, withdrawing said mixture from said zone anddirecting it to a precipitation zone; adding another stream of saidaqueous sodium hydroxide to said mixture in said precipitation zone at afourth rate of flow and in a suflicient quantity to precipitate themajor portion of the uranium values upon the completion of the nextsaidmixing step; mixing said another stream of hydroxide with said mixture;measuring the ratio of said third rate of flow to said fourth rate offlow and producing a ratio control signal by comparingsaid ratio with apreselected ratio; and changing said fourth rate of flow in response tosaid ratio control signal.

2. A process according to claim 1 further comprising maintaining thetemperature in said titration zone and in said precipitation zone in therange extending from 100 F. to 170 F. M

3. A process according to claim 1 further comprising maintaining thetemperature in said titration zone and in said precipitation zone in therange extending from 130 F. to 150 F.

4. A process according to claimv 1 wherein both streams of aqueoussodium hydroxide contain from 40 to 60 percent by weight of sodiumhydroxide.

5. An improved process for precipitating uranium values from a clarifiedpregnant liquor formed by leaching an ore with. a carbonate leachsolution, said process comprising feeding a stream of clarified pregnantliquor at a first rate of flow to a titration zone; feeding a stream ofaqueous sodium hydroxide at a second rate of flow to said titrationzone; mixing said hydroxide with said liquor in said zone to form amixture having a pH in the range from 10.8 to 11.7; measuring the pH ofsaid mixture and in response thereto producing a control signalrepresentative of the change in the rate of said feeding of saidhydroxide to produce a mixture of a preselected pH; changing said secondrate of fiow in response to said control signal; at a third rate offlow, withdrawing said mixture from said zone and directing it to aprecipitation zone; adding a second stream of said aqueous sodiumhydroxide to said mixture in said precipitation zone at a fourth rateor" flow and in a sufiicicnt quantity to precipitate the major portionof the uranium values upon the completion of the next-said mixing step;mixing said second stream of hydroxide with said mixture; measuring theratio of said first rate of flow to said fourth rate of flow andproducing another control si nal by comparing said ratio With apreselected ratio; and changing said fourth rate of flow in response tosaid another control signal.

6. A processing according to claim 5 further comparing maintaining thetemperature in said titration zone and in said precipitation zone in therange extending from F. to 170 F.

7. A process according to claim 5 further comprising maintain thetemperature in said titration zone and in said precipitation Zone in therange extending from F. to F.

8. A process according to claim 1 wherein both streams of aqueous sodiumhydroxide contain from 40 to 60 percent by weight of sodium hydroxide.

9. An improved process for precipitating uranium values from a clarifiedpregnant liquor formed by leaching an ore with a carbonate leachsolution said process comprising feeding a stream of clarified pregnantliquor at a first rate of flow to a titration zone; feeding a stream ofan alkali metal hydroxide at a second rate of flow to said titrationzone; mixing said hydroxide with said liquor in said zone to form amixture having a pH in the range from 10.8 to 11.7; measuring the pH ofsaid mixture and comparing it with a preselected pH in said range toproduce a control signal representative of the change in the rate ofsaid feeding of said hydroxide to produce a mixture of said preselectedpH; changing said second rate of flow in response to said controlsignal; at a third rate of flow, withdrawing said mixture from said zoneand directing it to a precipitation zone; adding another stream of analkali metal hydroxide to said mixture in said precipitation zone at afourth rate of flow and in a sufiicient quantity to precipitate themajor portion of the uranium values; measuring the ratio of one of saidfirst and third rates of flow to said fourth rate of flow and producinganother control signal by comparing said ratio with a. preselectedratio; and changing said fourth rate of flow in response to said anothercontrol signal.

10. A process according to claim 9 further comprising maintaining thetemperature in said titration zone and in said precipitation zone in therange extending from 100 F. to F.

11. A process according to claim 9 further comprising maintaining thetemperature in said titration zone and in said precipitation zone in therange extending from 130 F. to 150 F.

12. A process according to claim 9 wherein both streams of aqueoushydroxide consist essentially of the same alkali metal hydroxides.

13. A process according to claim 9 wherein both streams of aqueoushydroxide contain from 40 to 60 percent by weight of hydroxide.

14. An improved process for precipitating uranium values from aclarified pregnant liquor formed by leaching an ore with a carbonateleach solution, said process comprising feeding a stream of clarifiedpregnant liquor containing uranium values from 0.5 to 15 grams per literexpressed as U at a first rate of flow to a titration zone; feeding anaqueous solution containing 20 to 60 weight percent alkali metalhydroxide at a sec-0nd rate of flow to said titration zone to form amixture having a pH in the range from 10.8 to 11.7; measuring the pH ofsaid mixture and comparing it with a preselected pH in said range toproduce a control signal representative of the change in the rate ofsaid feeding of aqueous solution to produce a mixture of saidpreselected pH; changing said second rate of flow in response to saidcontrol signal; at a third rate of flow, withdrawing said mixture fromsaid zone and directing it to a precipitation zone; adding anotherstream of said aqueous solution to said mixture in said precipitationzone at a fourth rate of flow and in a sufficient quantity toprecipitate the major portion of the uranium values; measuring the ratioof said second rate of flow to one of said first and third rates of flowand producing another control signal by comparing said ratio with apreselected ratio; changing said fourth rate of flow in response to saidanother control signal; and maintaining a temperature in the rangeextending from 130 F. to 150 F. during the steps from the first-saidfeeding step to said changing step.

15. An improved process for precipitating uranium values from aclarified pregnant liquor formed by leaching an ore with a solution thatcomprises the carbonate and bicarbonate of a least one member selectedfrom the group consisting of alkali metals, said process comprisingfeeding a stream of clarified pregnant liquor at a first rate of flow toa titration zone; feeding a second stream of a hydroxide of at least onemember selected from the group consisting of sodium, potassium, lithium,rubidium, cesium, calcium, and magnesium at a second rate of flow tosaid titration zone; mixing said second stream With said liquor in saidzone to form a mixture having a pH in the range from 10.8 to 11.7;measuring the pH of said mixture and in response thereto producing acontrol signal representative of the change in the rate of said feedingof said second stream to produce a mixture of said preselected pH;changing said second rate of flow in response to said control signal; ata third rate of flow, Withdrawing said mixture from said zone anddirecting it to a precipitation zone; adding another stream of ahydroxide of at least one member selected from said group consisting ofalkali metals to the mixture in said precipitation zone at a fourth rateof flow and in la suflicient quantity to precipitate the major portionof the uranium values; measuring the ratio of one of said first andthird rates of flow to said fourth rate of flow and producing an- 10other control signal by comparing said ratio with a preselected ratio;and changing said fourth rate of flow in response to said anothercontrol signal.

16. A method according to claim 15 wherein said solution comprises oneselected from said group and the same member is selected from said groupin the secondsaid feeding step and said adding step.

17. In the carbonate leach process for recovering uranium values from aclarified pregnant solution by the addition of a precipitating agent tosaid solution, the improvement comprising adding said agent to saidsolution in first and second stages; automatically controlling theadding in said first stage by measuring the pH of the admixture with apH controller to produce a first control signal and adjusting the rateat which said agent is added in said first stage responsive to saidfirst control signal; and automatically controlling the adding in secondstage by measuring with a ratio controller the ratio of the rate atwhich said solution is fed into said first stage to the rate at whichsaid agent is added in said second stage to produce a second controlsignal and adjusting the rate at which said agent is added in saidsecond stage in response to said second control signal.

18. In the carbonate leach process for recovering uranium values from aclarified pregnant solution by the addition of a precipitating agent tosaid solution, the improvement comprising adding said agent to saidsolution in first and second stages, to form respectively, an admixtureand a precipitate; automatically controlling the adding in said firststage by measuring the pH of the admixture with a pH controller toproduce a first control signal and adjusting the rate at which saidagent is added in said first stage responsive to said first controlsignal; and automatically controlling the adding in said second stage bymeasuring With a ratio controller the ratio of the rate at which saidadmixture is fed into said second stage to the rate at which said agentis added in second stage to produce a second control signal andadjusting the rate at which said agent is added in said second stage inresponse to said second control signal.

References Cited in the file of this patent UNITED STATES PATENTS1,450,023 Edelman Mar. 27, 1923 1,945,611 Knight et al. Feb. .6, 19342,466,118 Miller .Apr. 5, 1949 2,702,238 Hays Feb. 15, 1955 2,779,657Ballard Jan. 29, 1957 2,813,003 Thunaes et a1 Nov. 12, 1957 2,841,468Wilson June 1, 1958 2,897,048 Stevenson July 28, 1959 OTHER REFERENCESBrown et al.; Chem. Eng. Progress Symposium Series, vol. 50, No. 13,pages 5-10 (1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,104,941 September 24 1963 James L. Hart et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 8, lines 2'? and 28, for "comparing" read comprising line 32, for"maintain" read maintaining line 35, for the claim reference numeral "1"read 5 Signed and sealed this 21st day of April 1964.

(SEAL) Attest: EDWARD J. BRENNER ERNEST W. SWIDER Attesting OfficerCommissioner of Patents

1. AN IMPROVED PROCESS FOR PRECIPITATING URANIUM VALUES FROM A CLARIFIEDPREGNANT LIQUOR FORMED BY LEACHING AN ORE WITH A CARBONATE LEACHSOLUTION, SAID PROCESS COMPRISING FEEDING A STREAM OF CLARIFIED PREGNANTLIQUOR AT A FIRST RATE OF FLOW TO A TITRATION ZONE; FEEDING A STREAM OFAQUEOUS SODIUM HYDROXIDE AT A SECOND RATE OF FLOW TO SAID TITRATIONZONE; MIXING SAID HYDROXIDE WITH SAID LIQUOR IN SAID ZONE TO FORM AMIXTURE HAVING A PH IN THE RANGE FROM 10.8 TO 11.7 MEASURING THE PH OFSAID MIXTURE AND COMPRISING IT WITH A PRESELECTED PH IN SAID RANGE TO TOPRODUCE A CONTROL SIGNAL REPRESENTATIVE OF THE CHANGE IN THE RATE OFSAID FEEDING OF HYDROXIDE TO PRODUCE A MIXTURE OF SAID PRESELECTED PH;CHANGING SAID SECOND RATE OF FLOW IN RESPONSE TO SAID CONTROL SIGNAL; ATA THIRD